Method of cutting semiconductor substrate

ABSTRACT

Multiphoton absorption is generated, so as to form a part which is intended to be cut  9  due to a molten processed region  13  within a silicon wafer  11,  and then an adhesive sheet  20  bonded to the silicon wafer  11  is expanded. This cuts the silicon wafer  11  along the part which is intended to be cut  9  with a high precision into semiconductor chips  25.  Here, opposing cut sections  25   a,    25   a  of neighboring semiconductor chips  25, 25  are separated from each other from their close contact state, whereby a die-bonding resin layer  23  is also cut along the part which is intended to be cut  9.  Therefore, the silicon wafer  11  and die-bonding resin layer  23  can be cut much more efficiently than in the case where the silicon wafer  11  and die-bonding resin layer  23  are cut with a blade without cutting a base  21.

TECHNICAL FIELD

The present invention relates to a method of cutting a semiconductorsubstrate used for cutting a semiconductor substrate in semiconductordevice manufacturing processes and the like.

BACKGROUND ART

As a conventional technique of this kind, Japanese Patent ApplicationLaid-Open Nos. 2002-158276 and 2000-104040 disclose the followingtechnique. First, an adhesive sheet is bonded to the rear face of asemiconductor wafer by way of a die-bonding resin layer, and thesemiconductor wafer is cut with a blade while in a state where thesemiconductor wafer is held on the adhesive sheet, so as to yieldsemiconductor chips. Subsequently, when picking up the semiconductorchips on the adhesive sheet, the die-bonding resin is peeled of togetherwith the individual semiconductor chips. This can bond the semiconductorchips onto a lead frame while omitting the step of applying an adhesiveto the rear faces of semiconductor chips, and so forth.

When cutting the semiconductor wafer held on the adhesive sheet with theblade in the above-mentioned technique, however, the die-bonding resinlayer existing between the semiconductor wafer and adhesive sheet isneeded to be cut surely without cutting the adhesive sheet. Therefore,particular care must be taken when cutting a semiconductor wafer with ablade in such a case.

DISCLOSURE OF THE INVENTION

In view of such circumstances, it is an object of the present inventionto provide a method of cutting a semiconductor substrate which canefficiently cut a semiconductor substrate with a die-bonding resinlayer.

For achieving the above-mentioned object, in one aspect, the presentinvention provides a method of cutting a semiconductor substrate, themethod comprising the steps of irradiating a semiconductor substratehaving a sheet bonded thereto by way of a die-bonding resin layer withlaser light while locating a light-converging point within thesemiconductor substrate, so as to form a modified region caused bymultiphoton absorption within the semiconductor substrate, and causingthe modified region to form a part which is intended to be cut; andexpanding the sheet after the step of forming the part which is intendedto be cut, so as to cut the semiconductor substrate and die-bondingresin layer along the part which is intended to be cut.

This method of cutting a semiconductor substrate irradiates thesemiconductor substrate with laser light while locating alight-converging point within the semiconductor substrate, and generatesa phenomenon of multiphoton absorption within the semiconductorsubstrate, so as to form a modified region, whereby the modified regioncan form a part which is intended to be cut within the semiconductorsubstrate along a desirable line to cut for cutting the semiconductorsubstrate. When the part which is intended to be cut is formed withinthe semiconductor substrate as such, a relatively small force can startfractures in the thickness direction of the semiconductor substrate fromthe part which is intended to be cut. Therefore, when the sheet bondedto the semiconductor substrate is expanded, the semiconductor substratecan be cut with a high precision along the part which is intended to becut. Here, opposing cut sections of the cut semiconductor substrate areinitially in close contact with each other, but are separated from eachother as the sheet expands, whereby the die-bonding resin layer existingbetween the semiconductor substrate and the sheet is also cut along thepart which is intended to be cut. Therefore, the semiconductor substrateand die-bonding resin layer can be cut along the part which is intendedto be cut much more efficiently than in the case where the semiconductorsubstrate and die-bonding resin layer are cut with a blade while leavingthe sheet. Also, since the opposing cut sections of the cutsemiconductor substrate are initially in close contact with each other,the cut pieces of the semiconductor substrate and cut pieces of thedie-bonding resin layer have substantially the same outer form, wherebythe die-bonding resin is prevented from protruding from the cut sectionsof the semiconductor substrate.

In another aspect, the present invention provides a method of cutting asemiconductor substrate, the method comprising the steps of irradiatinga semiconductor substrate having a sheet bonded thereto by way of adie-bonding resin layer with laser light while locating alight-converging point within the semiconductor substrate under acondition with a peak power density of at least 1×10⁸ (W/cm²) at thelight-converging point and a pulse width of 1 μs or less, so as to forma modified region including a molten processed region within thesemiconductor substrate, and causing the modified region including themolten processed region to form a part which is intended to be cut; andexpanding the sheet after the step of forming the part which is intendedto be cut, so as to cut the semiconductor substrate and die-bondingresin layer along the part which is intended to be cut.

This method of cutting a semiconductor substrate irradiates thesemiconductor substrate with laser light while locating alight-converging point within the semiconductor substrate under acondition with a peak power density of at least 1×10⁸ (W/cm²) at thelight-converging point and a pulse width of 1 μs or less. Therefore, theinside of the semiconductor substrate is locally heated by multiphotonabsorption. This heat forms a molten processed region within thesemiconductor substrate. Since the molten processed region is an exampleof the above-mentioned modified region, the semiconductor substrate anddie-bonding resin layer can also be cut along the part which is intendedto be cut much more efficiently in this method of cutting asemiconductor substrate than in the case where the semiconductorsubstrate and die-bonding resin layer are cut with a blade while leavingthe sheet.

In still another aspect, the present invention provides a method ofcutting a semiconductor substrate, the method comprising the steps ofirradiating a semiconductor substrate having a sheet bonded thereto byway of a die-bonding resin layer with laser light while locating alight-converging point within the semiconductor substrate, so as to forma modified region within the semiconductor substrate, and causing themodified region to form a part which is intended to be cut; andexpanding the sheet after the step of forming the part which is intendedto be cut, so as to cut the semiconductor substrate and die-bondingresin layer along the part which is intended to be cut. The modifiedregion may be a molten processed region.

Because of the same reason as with the above-mentioned methods ofcutting a semiconductor substrate, the semiconductor substrate anddie-bonding resin layer can also be cut along the part which is intendedto be cut much more efficiently in this method of cutting asemiconductor substrate than in the case where the semiconductorsubstrate and die-bonding resin layer are cut with a blade while leavingthe sheet. The modified region may be formed by multiphoton absorptionor other causes.

In still another aspect, the present invention provides a method ofcutting a semiconductor substrate, the method comprising the steps ofirradiating a semiconductor substrate having a sheet bonded thereto withlaser light while locating a light-converging point within thesemiconductor substrate, so as to form a modified region within thesemiconductor substrate, and causing the modified region to form a partwhich is intended to be cut; and expanding the sheet after the step offorming the part which is intended to be cut, so as to cut thesemiconductor substrate along the part which is intended to be cut.

This method of cutting a semiconductor substrate can cut thesemiconductor substrate along the part which is intended to be cut muchmore efficiently than in the case where the semiconductor substrate iscut with a blade while leaving the sheet.

In the step of forming the part which is intended to be cut in any ofthe above-mentioned methods of cutting a semiconductor substrate inaccordance with the present invention, a fracture may be caused to reacha front face of the semiconductor substrate on the laser light entranceside from the part which is intended to be cut acting as a start point,a fracture may be caused to reach a rear face of the semiconductorsubstrate on the side opposite from the laser light entrance side fromthe part which is intended to be cut acting as a start point, or afracture may be caused to reach the front face of the semiconductorsubstrate on the laser light entrance side and the rear face on the sideopposite therefrom from the part which is intended to be cut acting as astart point.

In still another aspect, the present invention provides a method ofcutting a semiconductor substrate, the method comprising the steps ofirradiating a semiconductor substrate having a sheet bonded thereto byway of a die-bonding resin layer with laser light while locating alight-converging point within the semiconductor substrate, so as to forma modified region caused by multiphoton absorption within thesemiconductor substrate, and causing the modified region to form a partwhich is intended to be cut; generating a stress in the semiconductorsubstrate along the part which is intended to be cut after the step offorming the part which is intended to be cut, so as to cut thesemiconductor substrate along the part which is intended to be cut; andexpanding the sheet after the step of cutting the semiconductorsubstrate, so as to cut the die-bonding resin layer along a cut sectionof the semiconductor substrate.

The modified region caused by multiphoton absorption can form a partwhich is intended to be cut within the semiconductor substrate along adesirable line to cut for cutting the semiconductor substrate in thismethod of cutting a semiconductor substrate as well. Therefore, when astress is generated in the semiconductor substrate along the part whichis intended to be cut, the semiconductor substrate can be cut with ahigh precision along the part which is intended to be cut. Then, whenthe sheet bonded to the semiconductor substrate is expanded, opposingcut sections of the cut semiconductor substrate are separated from eachother from their close contact state as the sheet expands, whereby thedie-bonding resin layer existing between the semiconductor substrate andsheet is cut along the cut sections of the semiconductor substrate.Therefore, the semiconductor substrate and die-bonding resin layer canbe cut along the part which is intended to be cut much more efficientlythan in the case where the semiconductor substrate and die-bonding resinlayer are cut with a blade while leaving the sheet. Also, since theopposing cut sections of the cut semiconductor substrate are initiallyin close contact with each other, the cut pieces of the semiconductorsubstrate and cut pieces of the die-bonding resin layer havesubstantially the same outer faun, whereby the die-bonding resin isprevented from protruding from the cut sections of the semiconductorsubstrate.

In still another aspect, the present invention provides a method ofcutting a semiconductor substrate, the method comprising the steps ofirradiating a semiconductor substrate having a sheet bonded thereto byway of a die-bonding resin layer with laser light while locating alight-converging point within the semiconductor substrate under acondition with a peak power density of at least 1×10⁸ (W/cm²) at thelight-converging point and a pulse width of 1 μs or less, so as to forma modified region caused by multiphoton absorption within thesemiconductor substrate, and causing the modified region to form a partwhich is intended to be cut; generating a stress in the semiconductorsubstrate along the part which is intended to be cut after the step offorming the part which is intended to be cut, so as to cut thesemiconductor substrate along the part which is intended to be cut; andexpanding the sheet after the step of cutting the semiconductorsubstrate, so as to cut the die-bonding resin layer along a cut sectionof the semiconductor substrate.

In still another aspect, the present invention provides a method ofcutting a semiconductor substrate, the method comprising the steps ofirradiating a semiconductor substrate having a sheet bonded thereto byway of a die-bonding resin layer with laser light while locating alight-converging point within the semiconductor substrate, so as to forma modified region within the semiconductor substrate, and causing themodified region to form a part which is intended to be cut; generating astress in the semiconductor substrate along the part which is intendedto be cut after the step of forming the part which is intended to becut, so as to cut the semiconductor substrate along the part which isintended to be cut; and expanding the sheet after the step of cuttingthe semiconductor substrate, so as to cut the die-bonding resin layeralong a cut section of the semiconductor substrate. The modified regionmay be a molten processed region.

Because of the same reason as with the above-mentioned methods ofcutting a semiconductor substrate, the semiconductor substrate anddie-bonding resin layer can also be cut along the part which is intendedto be cut much more efficiently in this method of cutting asemiconductor substrate than in the case where the semiconductorsubstrate and die-bonding resin layer are cut with a blade while leavingthe sheet.

In still another aspect, for achieving the above-mentioned object, thepresent invention provides a method of cutting a semiconductor substratehaving a front face formed with a functional device along a line to cut,the method comprising the steps of irradiating the semiconductorsubstrate with laser light while using a rear face of the semiconductorsubstrate as a laser light entrance surface and locating alight-converging point within the semiconductor substrate, so as to forma modified region, and causing the modified region to form a cuttingstart region within the semiconductor substrate inside of the laserlight entrance surface by a predetermined distance along the line tocut; attaching an expandable holding member to the rear face of thesemiconductor substrate by way of a die-bonding resin layer afterforming the cutting start region; and expanding the holding member afterattaching the holding member, so as to cut the semiconductor substrateand die-bonding resin layer along the line to cut.

The object to be processed in this method of cutting a semiconductorsubstrate is a semiconductor substrate having the front face formed witha functional device. Using the rear face of such a semiconductorsubstrate as a laser light entrance surface, the semiconductor substrateis irradiated with laser light while locating a light-converging pointwithin the semiconductor substrate, so as to generate multiphotonabsorption or optical absorption equivalent thereto, thereby forming acut start region caused by a modified region within the semiconductorsubstrate along the line to cut. Here, the rear face of thesemiconductor substrate is used as the laser light entrance surface,since there will be a fear of the functional device inhibiting the laserlight from entering if the front face is employed as the laser lightentrance surface. When the cutting start region is formed within thesemiconductor substrate as such, a fracture can start from the cuttingstart region naturally or with a relatively small force applied thereto,so as to reach the front and rear faces of the semiconductor substrate.Therefore, when an expandable holding member is attached to the rearface of the semiconductor substrate by way of a die-bonding resin layerand expanded after forming the cut start region, cut sections of thesemiconductor substrate cut along the lines to cut are separated fromeach other from their close contact state as the holding member expands.As a consequence, the die-bonding resin layer existing between thesemiconductor substrate and holding member is also cut along the line tocut. Therefore, the semiconductor substrate and die-bonding resin layercan be cut along the line to cut much more efficiently than in the caseof cutting with a blade or the like. Also, since the opposing cutsections of the cut semiconductor substrate are initially in closecontact with each other, the cut pieces of the semiconductor substrateand cut pieces of the die-bonding resin layer have substantially thesame outer form, whereby the die-bonding resin is prevented fromprotruding from the cut sections of the semiconductor substrate.

The functional device refers to semiconductor operating layers formed bycrystal growth, light-receiving devices such as photodiodes,light-emitting devices such as laser diodes, and circuit devices faintedas circuits, for example.

Preferably, the method further comprises the step of grinding the rearface of the semiconductor substrate such that the semiconductorsubstrate attains a predetermined thickness before forming the cuttingstart region. When the rear face of the semiconductor substrate isground beforehand such that tie semiconductor substrate attains apredetermined thickness as such, the semiconductor substrate anddie-bonding resin layer can be cut along the line to cut with a higherprecision. Here, the grinding encompasses cutting, polishing, chemicaletching, etc.

The modified region may include a molten processed region. When theobject to be processed is a semiconductor substrate, a molten processedregion may be formed upon in irradiation with laser light. Since themolten processed region is an example of the above-mentioned modifiedregion, the semiconductor substrate can be cut easily, whereby thesemiconductor substrate and die-bonding resin layer can efficiently becut along the line to cut in this case as well.

When forming the cutting start region in the above-mentioned methods ofcutting a semiconductor substrate in accordance with the presentinvention, a fracture may be caused to reach the front face of thesemiconductor substrate from the cutting start region acting as a startpoint, a fracture may be caused to reach the rear face of thesemiconductor substrate from the cutting start region acting as a startpoint, or a fracture may be caused to reach the front and rear faces ofthe semiconductor substrate from the cutting start region acting as astart point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor substrate during laserprocessing by the laser processing method in accordance with anembodiment;

FIG. 2 is a sectional view of the semiconductor substrate taken alongthe line II-II of FIG. 1;

FIG. 3 is a plan view of the semiconductor substrate after laserprocessing by the laser processing method in accordance with theembodiment;

FIG. 4 is a sectional view of the semiconductor substrate taken alongthe line IV-IV of FIG. 3;

FIG. 5 is a sectional view of the semiconductor substrate taken alongthe line V-V of FIG. 3;

FIG. 6 is a plan view of the semiconductor substrate cut by the laserprocessing method in accordance with the embodiment;

FIG. 7 is a view showing a photograph of a cross section in a part of asilicon wafer cut by the laser processing method in accordance with theembodiment;

FIG. 8 is a graph showing relationships between the laser lightwavelength and the transmittance within a silicon substrate in the laserprocessing method in accordance with the embodiment;

FIG. 9 is a schematic diagram of the laser processing apparatus inaccordance with an embodiment;

FIG. 10 is a flowchart for explaining a procedure of forming a partwhich is intended to be cut by the laser processing apparatus inaccordance with the embodiment;

FIGS. 11A and 11B are schematic views for explaining the method ofcutting a silicon wafer in accordance with an embodiment, in which FIG.11A shows a state where an adhesive sheet is bonded to the siliconwafer, whereas FIG. 11B shows a state where a part which is intended tobe cut due to a molten processed region is formed within the siliconwafer;

FIGS. 12A and 12B are schematic views for explaining the method ofcutting a silicon wafer in accordance with the embodiment, in which FIG.12A shows a state where the adhesive sheet is expanded, whereas FIG. 12Bshows a state where the adhesive sheet is irradiated with UV rays;

FIGS. 13A and 13B are schematic views for explaining the method ofcutting a silicon wafer in accordance with the embodiment, in which FIG.13A shows a state where a semiconductor chip is picked up together witha cut die-bonding resin layer, whereas FIG. 13B shows a state where thesemiconductor chip is joined to a lead frame by way of the die-bondingresin layer;

FIGS. 14A and 14B are schematic views showing relationships between thesilicon wafer and a part which is intended to be cut in the method ofcutting a silicon wafer in accordance with the embodiment, in which FIG.14A shows a state where no fractures are started from the part which isintended to be cut, whereas FIG. 14B shows a state where fracturesstarted from the part which is intended to be cut have reached the frontand rear faces of the silicon wafer;

FIGS. 15A and 15B are schematic views showing relationships between thesilicon wafer and a part which is intended to be cut in the method ofcutting a silicon wafer in accordance with the embodiment, in which FIG.15A shows a state where a fracture started from the part which isintended to be cut has reached the front face of the silicon wafer,whereas FIG. 15B shows a state where a fracture started from the partwhich is intended to be cut has reached the rear face of the siliconwafer;

FIGS. 16A and 16B are schematic views for explaining an example of themethod of cutting a silicon wafer in accordance with the embodiment, inwhich FIG. 16A shows a state immediately after starting expanding theadhesive sheet, whereas FIG. 16B shows a state during the expanding ofthe adhesive sheet;

FIGS. 17A and 17B are schematic views for explaining this example of themethod of cutting a silicon wafer in accordance with the embodiment, inwhich FIG. 17A shows a state after completing the expanding of theadhesive sheet, whereas FIG. 17B shows a state at the time of picking upa semiconductor chip;

FIG. 18 is a schematic view for explaining another example of the methodof cutting a silicon wafer in accordance with the embodiment;

FIGS. 19A and 19B are views for explaining a case where no fractures arestarted from a part which is intended to be cut in still another exampleof the method of cutting a silicon wafer in accordance with theembodiment, in which FIG. 19A shows a state after the part which isintended to be cut due to a molten processed region is formed, whereasFIG. 19B shows a state where the adhesive sheet is expanded;

FIGS. 20A and 20B are views for explaining a case where fracturesstarted from a part which is intended to be cut reach the front and rearfaces of the silicon wafer in this example of the method of cutting asilicon wafer in accordance with the embodiment, in which FIG. 20A showsa state after the part which is intended to be cut due to a moltenprocessed region is formed, whereas FIG. 20B shows a state where theadhesive sheet is expanded;

FIGS. 21A and 21B are views for explaining a case where a fracturestarted from a part which is intended to be cut reaches the front faceof the silicon wafer in this example of the method of cutting a siliconwafer in accordance with the embodiment, in which FIG. 21A shows a stateafter the part which is intended to be cut due to a molten processedregion is formed, whereas FIG. 21B shows a state where the adhesivesheet is expanded;

FIGS. 22A and 22B are views for explaining a case where a fracturestarted from a part which is intended to be cut reaches the rear face ofthe silicon wafer in this example of the method of cutting a siliconwafer in accordance with the embodiment, in which FIG. 22A shows a stateafter the part which is intended to be cut due to a molten processedregion is formed, whereas FIG. 22B shows a state where the adhesivesheet is expanded;

FIG. 23 is a plan view of a silicon wafer to become an object to beprocessed in the method of cutting a semiconductor substrate inaccordance with an embodiment;

FIGS. 24A to 24C are schematic views for explaining the method ofcutting a semiconductor substrate in accordance with the embodiment, inwhich FIG. 24A shows a state where a protective film is bonded to thesilicon wafer, FIG. 24B shows a state where the silicon wafer isthinned, and FIG. 24B shows a state where the protective film isirradiated with UV rays;

FIGS. 25A to 25C are schematic views for explaining the method ofcutting a semiconductor substrate in accordance with the embodiment, inwhich FIG. 25A shows a state where the silicon wafer and protective filmare fixed onto a mount table, FIG. 25B shows a state where the siliconwafer is irradiated with laser light, and FIG. 25C shows a state where acutting start region is formed within the silicon wafer;

FIGS. 26A to 26C are schematic views for explaining the method ofcutting a semiconductor substrate in accordance with the embodiment, inwhich FIG. 26A shows a state where a film with a die-bonding resin filmis bonded to the silicon wafer, FIG. 26B shows a state where theprotective film is peeled off from the silicon wafer, and FIG. 26C showsa state where an expandable film is irradiated with UV rays; and

FIGS. 27A to 27C are schematic views for explaining the method ofcutting a semiconductor substrate in accordance with the embodiment, inwhich FIG. 27A shows a state where the expandable film is expanded, FIG.27B shows a state where a semiconductor chip is picked up together witha cut die-bonding resin layer, and FIG. 27C shows a state where thesemiconductor chip is joined to a lead frame by way of the die-bondingresin layer.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of the method of cutting asemiconductor substrate in accordance with the present invention will beexplained in detail with reference to drawings.

The method of cutting a semiconductor substrate in accordance with anembodiment irradiates a semiconductor substrate with laser light whilelocating a light-converging point within the semiconductor substrate, soas to form a modified region caused by multiphoton absorption within thesemiconductor substrate, and causes the modified region to form a partwhich is intended to be cut. Therefore, before explaining the method ofcutting a semiconductor substrate in accordance with this embodiment, alaser processing method carried out for forming the part which isintended to be cut will be explained mainly in terms of multiphotonabsorption.

A material becomes optically transparent when its absorption bandgapE_(G) is greater than photon energy hv. Hence, a condition under whichabsorption occurs in the material is hv>E_(G). However, even whenoptically transparent, the material generates absorption under acondition of nhv>E_(G) (where n=2, 3, 4, . . . ) if the intensity oflaser light becomes very high. This phenomenon is known as multiphotonabsorption. In the case of pulsed waves, the intensity of laser light isdetermined by the peak power density (W/cm²) of laser light at alight-converging point. The multiphoton absorption occurs under acondition where the peak power density is 1×10⁸ (W/cm²) or greater, forexample. The peak power density is determined by (energy of laser lightat the light-converging point per pulse)/(beam spot cross-sectional areaof laser light×pulse width). In the case of continuous waves, theintensity of laser light is determined by the field intensity (W/cm²) oflaser light at the light-converging point.

The principle of the laser processing method in accordance with anembodiment using such multiphoton absorption will be explained withreference to FIGS. 1 to 6. FIG. 1 is a plan view of a semiconductorsubstrate 1 during laser processing. FIG. 2 is a sectional view of thesemiconductor substrate 1 taken along the line of FIG. 1. FIG. 3 is aplan view of the semiconductor substrate 1 after the laser processing.FIG. 4 is a sectional view of the semiconductor substrate 1 taken alongthe line IV-IV of FIG. 3. FIG. 5 is a sectional view of thesemiconductor substrate 1 taken along the line V-V of FIG. 3. FIG. 6 isa plan view of the cut semiconductor substrate 1.

As shown in FIGS. 1 and 2, a desirable line to cut 5 exists on a frontface 3 of the semiconductor substrate 1. The line to cut 5 is a virtualline extending straight (although a line may actually be drawn on thesemiconductor substrate 1 so as to become the line to cut 5). The laserprocessing in accordance with this embodiment irradiates thesemiconductor substrate 1 with laser light while locating alight-converging point P within the semiconductor substrate 1 under acondition generating multiphoton absorption, so as to form a modifiedregion 7. The light-converging point is a position at which the laserlight L is converged.

The laser light L is relatively moved along the line to cut 5 (i.e.,along the direction of arrow A), so as to shift the light-convergingpoint P along the line to cut 5. As a consequence, the modified region 7is formed along the line to cut 5 only within the semiconductorsubstrate 1 as shown in FIGS. 3 to 5, and a part which is intended to becut 9 is formed by the modified region 7. In the laser processing methodin accordance with this embodiment, the modified region 7 is not formedby the heat generated from the semiconductor substrate 1 absorbing thelaser light L. The laser light L is transmitted through thesemiconductor substrate 1, so as to generate multiphoton absorptiontherewithin, thereby forming the modified region 7. Therefore, the frontface 3 of the semiconductor substrate 1 hardly absorbs the laser light Land does not melt.

When a start point exists in an area for cutting the semiconductorsubstrate 1, the semiconductor substrate 1 fractures from this startpoint, whereby the semiconductor substrate 1 can be cut with arelatively small force as shown in FIG. 6. Hence, the semiconductorsubstrate 1 can be cut without generating unnecessary fractures in thefront face 3 of the semiconductor substrate 1.

There seem to be the following two ways of cutting a semiconductorsubstrate from a cutting start region acting as a start point. The firstcase is where an artificial force is applied to the semiconductorsubstrate after the cutting start region is formed, so that thesemiconductor substrate fractures from the cutting start region actingas a start point, and thus is cut. This is the cutting in the case wherethe semiconductor substrate has a large thickness, for example. Applyingan artificial force refers to exerting a bending stress or shear stressto the semiconductor substrate along the cutting start region, orgenerating a thermal stress by imparting a temperature difference to thesemiconductor substrate, for example. The other case is where theforming of the cutting start region causes the semiconductor substrateto fracture naturally in its cross-sectional direction (thicknessdirection) from the cutting start region acting as a start point,thereby cutting the semiconductor substrate. This becomes possible ifthe cutting start region is formed by one row of the modified regionwhen the semiconductor substrate has a small thickness, or if thecutting start region is formed by a plurality of rows of the modifiedregion in the thickness direction when the semiconductor substrate has alarge thickness. Even in this naturally fracturing case, fractures donot extend onto the front face at a portion corresponding to an area notformed with the cutting start region in the part which is intended to becut, so that only the portion corresponding to the area formed with thecutting start region can be cleaved, whereby cleavage can be controlledwell. Such a cleaving method with a favorable controllability is quiteeffective, since semiconductor substrates such as silicon wafers haverecently been apt to decrease their thickness.

An example of the modified region formed by multiphoton absorption inthis embodiment is a molten processed region which will be explained inthe following.

A semiconductor substrate is irradiated with laser light while locatinga light-converging point therewithin under a condition with a fieldintensity of at least 1×10⁸ (W/cm²) at the light-converging point and apulse width of 1 μs or less. As a consequence, the inside of the objectis locally heated by multiphoton absorption. This heating forms a moltenprocessed region within the object. The molten processed regionencompasses regions once molten and then re-solidified, regions just ina molten state, and regions in the process of being re-solidified fromthe molten state, and can also be referred to as a region whose phasehas changed or a region whose crystal structure has changed. The moltenprocessed region may also be referred to as a region in which a certainstructure changes to another structure among monocrystal, amorphous, andpolycrystal structures. For example, it means a region having changedfrom the monocrystal structure to the amorphous structure, a regionhaving changed from the monocrystal structure to the polycrystalstructure, or a region having changed from the monocrystal structure toa structure containing amorphous and polycrystal structures. When theobject to be processed is of a silicon monocrystal structure, the moltenprocessed region is an amorphous silicon structure, for example. Theupper limit of field intensity is 1×10¹² (W/cm²), for example. The pulsewidth is preferably 1 to 200 ns, for example.

By an experiment, the inventors verified that a molten processed regionwas formed within a silicon wafer. The following are conditions of theexperiment.

(A) Object to be processed: silicon wafer (with a thickness of 350 μmand an outer diameter of 4 inches)

(B) Laser

light source: semiconductor laser pumping Nd:YAG laser

wavelength: 1064 nm

laser light spot cross-sectional area: 3.14×10⁻⁸ cm²

oscillation mode: Q-switched pulse

repetition frequency: 100 kHz

pulse width: 30 ns

output: 20 μJ/pulse

laser light quality: TEM₀₀

polarizing property: linear polarization

(C) Condenser lens

magnification: ×50

N.A.: 0.55

transmittance at a laser light wavelength: 60%

(D) Moving rate of the mount table mounting the object: 100 mm/sec

FIG. 7 is a view showing a photograph of a cross section of a part of asilicon wafer cut by laser processing under the conditions mentionedabove. A molten processed region 13 is formed within the silicon wafer11. The molten processed region 13 formed under the above-mentionedconditions has a size of about 100 μm in the thickness direction.

The fact that the molten processed region 13 is formed by multiphotonabsorption will now be explained. FIG. 8 is a graph showingrelationships between the laser light wavelength and the transmittancewithin the silicon substrate. Here, the respective reflected componentson the front and rear sides of the silicon substrate are eliminated, soas to show the internal transmittance alone. The respectiverelationships are shown in the cases where the thickness t of thesilicon substrate is 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.

For example, at the Nd:YAG laser wavelength of 1064 nm, the laser lightappears to be transmitted through the silicon substrate by at least 80%when the silicon substrate has a thickness of 500 μm or less. Since thesilicon wafer 11 shown in FIG. 7 has a thickness of 350 μm, the moltenprocessed region 13 caused by multiphoton absorption is formed near thecenter of the silicon wafer 11, i.e., at a part distanced from the frontface by 175 μm. The transmittance in this case is 90% or more withreference to a silicon wafer having a thickness of 200 μm, whereby thelaser light is absorbed only slightly within the silicon wafer 11 but issubstantially transmitted therethrough. This means that the moltenprocessed region 13 is formed within the silicon wafer 11 not by laserlight absorption within the silicon wafer 11 (i.e., not by usual heatingwith the laser light) but by multiphoton absorption. The forming of amolten processed region by multiphoton absorption is disclosed, forexample, in “Silicon Processing Characteristic Evaluation by PicosecondPulse Laser”, Preprints of the National Meetings of Japan WeldingSociety, Vol. 66 (April, 2000), pp. 72-73.

A fracture is generated in a silicon wafer from a cutting start regionformed by a molten processed region, acting as a start point, toward across section, and reaches the front and rear faces of the siliconwafer, whereby the silicon wafer is cut. The fracture reaching the frontand rear faces of the silicon wafer may grow naturally or as a force isapplied to the silicon wafer. The fracture naturally growing from thecutting start region to the front and rear faces of the silicon waferencompasses a case where the fracture grows from a state where themolten processed region forming the cutting start region is molten and acase where the fracture grows when the molten processed region formingthe cutting start region is re-solidified from the molten state. Ineither case, the molten processed region is formed only within thesilicon wafer, and thus is present only within the cut section aftercutting as shown in FIG. 7. When a cutting start region is formed withinthe object by a molten processed region as such, unnecessary fracturesdeviating from a cutting start region line are harder to occur at thetime of cleaving, whereby cleavage control becomes easier.

When a cutting start region is formed as follows while taking account ofthe crystal structure of a semiconductor substrate, its cleavagecharacteristic, and the like, the object can be cut with a highprecision by a smaller force from the cutting start region acting as astart point.

Namely, in the case of a substrate made of a monocrystal semiconductorhaving a diamond structure such as silicon, it will be preferred if acutting start region is formed in a direction extending along a (111)plane (first cleavage plane) or a (110) plane (second cleavage plane).In the case of a substrate made of a III-V family compound semiconductorof sphalerite structure such as GaAs, it will be preferred if a cuttingstart region is formed in a direction extending along a (110) plane.

When the substrate is formed with an orientation flat in a direction tobe formed with the above-mentioned cutting start region (e.g., adirection extending along a (111) plane in a monocrystal siliconsubstrate) or a direction orthogonal to the direction to be formedtherewith, the cutting start region extending in the direction to beformed with the cutting start region can be formed easily and accuratelywith reference to the orientation flat.

With reference to FIG. 9, a laser processing apparatus used in theabove-mentioned laser processing method will now be explained. FIG. 9 isa schematic diagram of a laser processing apparatus 100.

The laser processing apparatus 100 comprises a laser light source 101for generating laser light L; a laser light source controller 102 forcontrolling the laser light source 101 in order to regulate the output,pulse width, and the like of the laser light L; a dichroic mirror 103arranged so as to change the orientation of the optical axis of thelaser light L by 90° while functioning to reflect the laser light L; acondenser lens 105 for converging the laser light L reflected by thedichroic mirror 103; a mount table 107 for mounting a semiconductorsubstrate 1 to be irradiated with the laser light L converged by thecondenser lens 105; an X-axis stage 109 for moving the mount table 107along an X axis; a Y-axis stage 111 for moving the mount table 107 alonga Y axis which is orthogonal to the X axis; a Z-axis stage 113 formoving the mount table 107 along a Z-axis which is orthogonal to X and Yaxes; and a stage controller 115 for controlling the movement of thethree stages 109, 111, 113.

The Z axis is orthogonal to the front face 3 of the semiconductorsubstrate 1, and thus is the direction of focal depth of the laser lightincident on the semiconductor substrate 1. Therefore, thelight-converging point P of the laser light L can be positioned withinthe semiconductor substrate 1 by moving the Z-axis stage 113 along the Zaxis. The movement of the light-converging point P along the X (Y) axisis performed by moving the semiconductor substrate 1 along the X (Y)axis by the X (Y)-axis stage 109 (111).

The laser light source 101 is Nd:YAG laser generating pulsed laserlight. Other examples of the laser employable in the laser light source101 include Nd:YVO₄ laser, Nd:YLF laser, and titanium sapphire laser.For forming a molten processed region, Nd:YAG laser, Nd:YVO₄ laser, andNd:YLF laser are preferably used. Though this embodiment uses pulsedlaser light for processing the semiconductor substrate 1, continuouswave laser light may also be used if it can cause multiphotonabsorption.

The laser processing apparatus 100 further comprises an observationlight source 117 for generating visible rays for illuminating thesemiconductor substrate 1 mounted on the mount table 107, and a visibleray beam splitter 119 disposed on the same optical axis as with thedichroic mirror 103 and condenser lens 105. The dichroic mirror 103 isdisposed between the beam splitter 119 and condenser lens 105. The beamsplitter 119 functions to reflect about a half of the visible rays andtransmit the remaining half therethrough, and is disposed so as tochange the orientation of the optical axis of visible rays by 90°. Abouta half of the visible rays generated from the observation light source117 are reflected by the beam splitter 119. Thus reflected visible rayspass through the dichroic mirror 103 and condenser lens 105, therebyilluminating the front face 3 of the semiconductor substrate 1 includingthe line to cut 5 and the like.

The laser processing apparatus 100 further comprises an image pickupdevice 121 and an imaging lens 123 which are disposed on the sameoptical axis as with the beam splitter 119, dichroic mirror 103, andcondenser lens 105. An example of the image pickup device 121 is a CCDcamera. The reflected light of visible rays having illuminated the frontface 3 of the semiconductor substrate 1 including the line to cut 5 andthe like passes through the condenser lens 105, dichroic minor 103, andbeam splitter 119, so as to be focused by the imaging lens 123 andcaptured by the image pickup device 121, thus yielding imaging data.

The laser processing apparatus 100 further comprises an imaging dataprocessor 125 for inputting the imaging data outputted from the imagepickup device 121, an overall controller 127 for controlling the laserprocessing apparatus 100 as a whole, and a monitor 129. Based on theimaging data, the imaging data processor 125 calculates focal data forpositioning the focal point of visible rays generated by the observationlight source 117 onto the front face 3. According to the focal data, thestage controller 115 regulates the movement of the Z-axis stage 113, soas to position the focal point of visible rays at the front face 3.Thus, the imaging data processor 125 functions as an autofocus unit. Onthe basis of imaging data, the imaging data processor 125 calculatesimage data such as enlarged images of the front face 3. The image dataare sent to the overall controller 127, so as to be subjected to variousprocessing operations, and thus processed data are transmitted to themonitor 129. As a consequence, enlarged images and the like aredisplayed on the monitor 129.

The data from the stage controller 115, the image data from the imagingdata processor 125, etc. are fed into the overall controller 127,whereas the laser light source controller 102, observation light source117, and stage controller 115 are regulated according to these data aswell, whereby the laser processing apparatus 100 as a whole iscontrolled. Hence, the overall controller 127 functions as a computerunit.

A procedure by which thus configured laser processing apparatus 100forms a part which is intended to be cut will now be explained withreference to FIGS. 9 and 10. FIG. 10 is a flowchart for explaining theprocedure by which thus configured laser processing apparatus 100 formsa part which is intended to be cut.

The light absorption characteristic of the semiconductor substrate 1 ismeasured by a spectrophotometer or the lake which is not depicted.According to the result of measurement, a laser light source 101generating laser light L having a wavelength to which the semiconductorsubstrate 1 is transparent or less absorptive is chosen (S101).Subsequently, the thickness of the semiconductor substrate 1 ismeasured. According to the result of measurement of thickness and therefractive index of the semiconductor substrate 1, the amount ofmovement of the semiconductor substrate along the Z axis is determined(S103). This is an amount of movement the semiconductor substrate 1along the Z axis with reference to the light-converging point P of laserlight positioned at the front face 3 of the semiconductor substrate 1for locating the light-converging point P of laser light L within thesemiconductor substrate 1. This amount of movement is fed into theoverall controller 127.

The semiconductor substrate 1 is mounted on the mount table 107 of thelaser processing apparatus 100. Then, visible rays are generated fromthe observation light source 117, so as to illuminate the semiconductorsubstrate 1 (S105). The font face 3 of the semiconductor substrate 1including the illuminated line to cut 5 is captured by the image pickupdevice 121. The line to cut 5 is a desirable virtual line to cut thesemiconductor substrate 1. The imaging data captured by the image pickupdevice 121 is sent to the imaging data processor 125. According to theimaging data, the imaging data processor 125 calculates such focal dataas to position the focal point of visible rays generated by theobservation light source 117 onto the front face 3 (S107).

The focal data is sent to the stage controller 115. According to thefocal data, the stage controller 115 moves the Z-axis stage 113 alongthe Z axis (S109). As a consequence, the focal point of the visible raysfrom the observation light source 117 is positioned at the front face 3of the semiconductor substrate 1. According to the imaging data, theimaging data processor 125 calculates enlarged image data of the frontface 3 of the semiconductor substrate 1 including the line to cut 5. Theenlarged image data is sent to the monitor 129 by way of the totalcontroller 127, whereby an enlarged image of the line to cut 5 and itsvicinity is displayed on the monitor 129.

The movement amount data determined by step S103 has been fed into thetotal controller 127 beforehand, and is sent to the stage controller115. According to the movement amount data, the stage controller 115causes the Z-axis stage 113 to move the semiconductor substrate 1 alongthe Z axis to such a position that the light-converging point P of laserlight L is located within the semiconductor substrate 1 (S111).

Subsequently, laser light L is generated from the laser light source101, so as to illuminate the line to cut 5 in the front face 3 of thesemiconductor substrate 1. Since the light-converging point P of laserlight L is located within the semiconductor substrate 1, a moltenprocessed region is formed only within the semiconductor substrate 1.Then, the X-axis stage 109 and Y-axis stage 111 are moved along the lineto cut 5, whereby the molten processed region formed along the line tocut 5 fowls a part which is intended to be cut along the line to cut 5(S113).

The foregoing completes the forming of the part which is intended to becut by the laser processing apparatus 100, whereby the part which isintended to be cut is formed within the semiconductor substrate 1. Whenthe part which is intended to be cut is formed within the semiconductorsubstrate 1, a relatively small force can start fractures in thethickness direction of the semiconductor substrate 1 from the part whichis intended to be cut.

The method of cutting a semiconductor substrate in accordance with thisembodiment will now be explained. Here, a silicon wafer 11 which is asemiconductor wafer is used as the semiconductor substrate.

First, as shown in FIG. 11A, an adhesive sheet 20 is bonded to the rearface 17 of the silicon wafer 11 so as to cover the rear face 17. Theadhesive sheet 20 includes a base 21 having a thickness of about 100 μm,on which a UV-curable resin layer 22 having a thickness on the order ofseveral micrometers is disposed. Further, on the UV-curable resin layer22, a die-bonding resin layer 23 functioning as a die-bonding adhesiveis disposed. A plurality of functional devices are formed like a matrixon the front face 3 of the silicon wafer 11. The functional devicerefers to a light-receiving device such as photodiode, a light-emittingdevice such as laser diode, a circuit device formed as a circuit, or thelike.

Subsequently, as shown in FIG. 11B, the silicon wafer 11 is irradiatedwith laser light from the front face 3 side by using the above-mentionedlaser processing apparatus 100, for example, such that thelight-converging point is located within the silicon wafer 11. As aconsequence, a molten processed region 13, which is a modified region,is formed within the silicon wafer 11, whereby a part which is intendedto be cut 9 is formed. In the forming of the part which is intended tobe cut 9, the laser light is emitted so as to run between a plurality offunctional devices arranged like a matrix on the front face 3 of thesilicon wafer 11, whereby the part which is intended to be cut 9 isformed like a grid running directly under between neighboring functionaldevices.

After forming the part which is intended to be cut 9, sheet expandingmeans 30 pulls the periphery of the adhesive sheet 20 outward as shownin FIG. 12A, thereby expanding the adhesive sheet 20. Expanding theadhesive sheet 20 starts fractures in the thickness direction from thepart which is intended to be cut 9, and the fractures reach the frontface 3 and rear face 17 of the silicon wafer 11. As a consequence, thesilicon wafer 11 is cut into the functional devices with a highprecision, whereby semiconductor chips 25 each having one functionaldevice are obtained.

Here, opposing cut sections 25 a, 25 a of neighboring semiconductorchips 25, 25 are initially in close contact with each other, but areseparated from each other as the adhesive sheet 20 expands, whereby thedie-bonding resin layer 23 in close contact with the rear face 17 of thesilicon wafer 11 is cut along the part which is intended to be cut 9.

There are cases where the sheet expanding means 30 is disposed on astage for mounting the silicon wafer 11 when forming the line to cut 9,and not. In the case where the sheet expanding means 30 is not disposedon the stage, transfer means transfers the silicon wafer 11 mounted onthe stage onto another stage provided with the sheet expanding means 30after forming the part which is intended to be cut 9.

After the expanding of the adhesive sheet 20 is completed, the adhesivesheet 20 is irradiated with UV rays from the rear face side as shown inFIG. 12B, whereby the UV-curable resin layer 22 is cured. This lowersthe adhesive force between the UV-curable resin layer 22 and die-bondingresin layer 23. The in irradiation with the UV rays may be performedbefore the expanding of the adhesive sheet 20 begins as well.

Subsequently, as shown in FIG. 13A, a vacuum collet or the like, whichis pickup means, is used for successively picking up the semiconductorchips 25. Here, the die-bonding resin layer 23 is cut into outer formssimilar to those of the semiconductor chips 25, whereas the adhesiveforce between the die-bonding resin layer 23 and UV-curable resin layer22 is lowered, whereby each semiconductor chip 25 is picked up while ina state where the cut die-bonding resin layer 23 is attached to its rearface. Then, as shown in FIG. 13B, the semiconductor chip 25 is mountedon a die pad of a lead frame 27 by way of the die-bonding resin layer 23closely in contact with the rear face, and is joined thereto with thefiller upon heating

In the method of cutting the silicon wafer 11, the molten processedregion 13 formed by multiphoton absorption yields the line to cut 9within the silicon wafer 11 along a desirable line to cut for cuttingthe silicon wafer 11 as in the foregoing. Therefore, when the adhesivesheet 20 bonded to the silicon wafer 11 is expanded, the silicon wafer11 is cut along the part which is intended to be cut 9 with a highprecision, whereby the semiconductor chips 25 are obtained. Here, theopposing cut sections 25 a, 25 a of the neighboring semiconductorsubstrates 25, 25 are initially in close contact with each other, butare separated from each other as the adhesive sheet 20 expands, wherebythe die-bonding resin layer 23 in close contact with the rear face 17 ofthe silicon wafer 11 is cut along the part which is intended to be cut9. Therefore, the silicon wafer 11 and die-bonding resin layer 23 can becut along the part which is intended to be cut 9 much more efficientlythan in the case where the silicon wafer 11 and die-bonding resin layer23 are cut with a blade without cutting the base 21.

Also, since the opposing cut sections 25 a, 25 a of the neighboringsemiconductor chips 25, 25 are initially in close contact with eachother, the cut individual semiconductor chips 25 and cut pieces of thedie-bonding resin layer 23 have substantially the same outer form,whereby the die-bonding resin is prevented from protruding from the cutsections 25 a of the semiconductor chips 25.

Though the foregoing method of cutting the silicon wafer 11 relates to acase where fractures starting from the part which is intended to be cut9 are not generated in the silicon wafer 11 before the adhesive sheet 20is expanded as shown in FIG. 14A, fractures 15 may be started from thepart which is intended to be cut 9 so as to reach the front face 3 andrear face 17 of the silicon wafer 11 as shown in FIG. 14B beforeexpanding the adhesive sheet 20. Examples of methods of generating thefractures 15 include one in which stress applying means such as a knifeedge is pressed against the rear face 17 of the silicon wafer 11 alongthe part which is intended to be cut 9 so as to cause a bending stressor shear stress in the silicon wafer 11 along the part which is intendedto be cut 9, and one in which a temperature difference is given to thesilicon wafer. 11 so as to generate a thermal stress in the siliconwafer 11 along the part which is intended to be cut 9.

When a stress is generated in the silicon wafer 11 along the part whichis intended to be cut 9 after forming the part which is intended to becut 9, so as to cut the silicon wafer 11 along the part which isintended to be cut 9 as such, semiconductor chips 25 cut with a veryhigh precision can be obtained. When the adhesive sheet 20 bonded to thesilicon wafer 11 is expanded, the opposing cut sections 25 a, 25 a ofthe neighboring semiconductor substrates 25, 25 are separated from eachother from their close contact state as the adhesive sheet 20 expands,whereby the die-bonding resin layer 23 in close contact with the rearface 17 of the silicon wafer 11 is cut along the cut sections 25 a inthis case as well. Therefore, the silicon wafer 11 and die-bonding resinlayer 23 can also be cut along the part which is intended to be cut 9much more efficiently by this cutting method than in the case where thesilicon wafer 11 and die-bonding resin layer 23 are cut with a bladewithout cutting the base 21.

When the silicon wafer 11 becomes thinner, there is a case wherefractures 15 started from the part which is intended to be cut 9 reachthe front face 3 and rear face 17 of the silicon wafer 11 as shown inFIG. 14B without causing a stress along the part which is intended to becut 9.

When the part which is intended to be cut 9 caused by the moltenprocessed region 13 is formed near the front face 3 within the siliconwafer 11 such that a fracture 15 reaches the front face 3 as shown inFIG. 15A, the cutting accuracy of the front face (i.e., functionaldevice forming surface) of the semiconductor chips 25 obtained bycutting can be made very high. When the part which is intended to be cut9 caused by the molten processed region 13 is formed near the rear face17 within the silicon wafer 11 such that a fracture 15 reaches the rearface 17 as shown in FIG. 15B, on the other hand, the die-bonding resinlayer 23 can be cut with a high precision by expanding the adhesivesheet 20.

Results of an experiment in a case using “LE-5000 (product name)”available from Lintec Corporation as the adhesive sheet 20 will now beexplained. FIGS. 16 and 17 are schematic views showing a series ofstates in the case where the adhesive sheet 20 is expanded after thepart which is intended to be cut 9 caused by the molten processed region13 is formed within the silicon wafer 11. Namely, FIG. 16A shows thestate immediately after starting expanding the adhesive sheet 20, FIG.16B shows the state in the process of expanding, FIG. 17A shows thestate after the expanding of the adhesive sheet 20 is completed, andFIG. 17B shows the state at the time of picking up the semiconductorchip 25.

Immediately after starting expanding the adhesive sheet 20, the siliconwafer 11 was cut along the part which is intended to be cut 9, wherebythe opposing cut sections 25 a, 25 a of neighboring semiconductor chips25 were in close contact with each other as shown in FIG. 16A. Here, thedie-bonding resin layer 23 had not been cut yet. Then, as the adhesivesheet 20 expanded, the die-bonding resin layer 23 was torn apart so asto be cut along the part which is intended to be cut 9 as shown in FIG.16B.

When the expanding of the adhesive sheet 20 was completed as such, thedie-bonding resin layer 23 was cut into the individual semiconductorchips 25 as shown in FIG. 17A. Here, a part 23 b of the die-bondingresin layer 23 was left thinly on the base 21 of the adhesive sheet 20between the semiconductor chips 25, 25 separated from each other. Thecut section 23 a of the die-bonding resin layer 23 cut together with thesemiconductor chip 25 was slightly recessed with reference to the cutsection 25 a of the semiconductor chip 25. This reliably prevented thedie-bonding resin from protruding from the cut sections 25 a of thesemiconductor chips 25. Then, the semiconductor chip 25 could be pickedup together with the cut die-bonding resin layer 23 by a vacuum colletor the like as shown in FIG. 17B.

When made of a nonelastic material and the like, the die-bonding resinlayer 23 is not left on the base 21 of the adhesive sheet 20 between thesemiconductor chips 25, 25 separated from each other as shown in FIG.18. Consequently, the cut section 25 a of the semiconductor chip 25 andthe cut section 23 a of the die-bonding resin layer 23 in close contactwith the rear face thereof can substantially coincide with each other.

The adhesive sheet 20 comprising the base 21 and UV-curable resin layer22 may be bonded to the rear face 17 of the silicon wafer 11 by way ofthe UV-curable resin layer 22 as shown in FIG. 19A, so as to form thepart which is intended to be cut 9 caused by the molten processed region13, and then the periphery of the adhesive sheet 20 may be extendedoutward as shown in FIG. 19B, so as to cut the silicon wafer 11 into thesemiconductor chips 25. The silicon wafer 11 can also be cut along thepart which is intended to be cut 9 with a high precision much moreefficiently in this case than in the case where the silicon wafer 11 iscut with a blade while leaving the adhesive sheet 20.

The method of cutting the silicon wafer 11 by using the adhesive sheet20 comprising the base 21 and UV-curable resin layer 22 is not limitedto the case where no fractures starting from the part which is intendedto be cut 9 occur in the silicon wafer 11 before expanding the adhesivesheet 20 as explained with reference to FIG. 19, but fractures 15started from the part which is intended to be cut 9 may be allowed toreach the front face 3 and rear face 17 of the silicon wafer 11 (FIG.20A) before expanding the adhesive sheet 20 (FIG. 20B) as shown in FIGS.20A and 20B. Also, a fracture 15 started from the part which is intendedto be cut 9 may be allowed to reach the front face 3 of the siliconwafer 11 (FIG. 21A) before expanding the adhesive sheet 20 (FIG. 21B) asshown in FIG. 21, or a fracture 15 started from the part which isintended to be cut 9 may be allowed to reach the rear face 17 of thesilicon wafer 11 (FIG. 22A) before expanding the adhesive sheet 20 (FIG.22B) as shown in FIG. 22.

In the following, a preferred second embodiment of the method of cuttinga semiconductor substrate in accordance with the present invention willbe explained more specifically. FIGS. 24 to 27 are partly sectionalviews of the silicon wafer taken along the line of FIG. 23.

On the front face 3 of a silicon wafer (semiconductor substrate) 11 tobecome an object to be processed, a plurality of functional devices 215are patterned into a matrix in directions parallel and perpendicular toan orientation flat 16 as shown in FIG. 23. In the following manner,such a silicon wafer 11 is cut into the functional devices 215.

First, as shown in FIG. 24A, a protective film 18 is bonded to thesilicon wafer 11 on, the front face 3 side, so as to cover thefunctional devices 215. The protective film 18 protects the functionaldevices 215 and holds the silicon wafer 11. After bonding the protectivefilm 18, the rear face 17 of the silicon wafer 11 is ground to a planesuch that the silicon wafer 11 attains a predetermined thickness, and isfurther subjected to chemical etching, so as to be smoothed as shown inFIG. 24B. As such, for example, the silicon wafer 11 having a thicknessof 350 μm is thinned to a thickness of 100 μm. After the silicon wafer11 is thinned, the protective film 18 is irradiated with UV rays. Thishardens the UV-curable resin layer, which is an adhesive layer in theprotective film 18, thereby making it easier for the protective film 18to peel off.

Subsequently, using a laser processing apparatus, a cutting start regionis formed within the silicon wafer 11. Namely, as shown in FIG. 25A, theprotective film 18 is secured onto the mount table 19 of the laserprocessing apparatus by vacuum suction such that the rear face 17 of thesilicon wafer 11 faces up, and lines to cut 5 are set like grids so asto pass between neighboring functional devices 215, 215 (seedash-double-dot lines in FIG. 23). Then, as shown in FIG. 25B, thesilicon wafer 11 is irradiated with laser light L while using the rearface 17 as a laser light entrance surface and locating thelight-converging point P within the silicon wafer 11 under a conditiongenerating the above-mentioned multiphoton absorption, and the mounttable 19 is moved, such that the light-converging point P is relativelyshifted along the lines to cut 5. Consequently, as shown in FIG. 25C,cutting start regions 8 are formed by molten processed regions 13 withinthe silicon wafer 11 along the lines to cut 5.

Next, the silicon wafer 11 having the protective film 18 bonded theretois removed from the mount table 19, and a die-bonding-resin-attachedfilm 220 (e.g., “LE-5000 (product name)” available from LintecCorporation) is bonded to the rear face 17 of the silicon wafer 11 asshown in FIG. 26A. The die-bonding-resin-attached film 220 includes anexpandable film (holding member) 221 having a thickness of about 100 μm,whereas a die-bonding resin layer 223 functioning as a die-bondingadhesive is disposed on the expandable film 221 by way of a UV-curableresin layer having a thickness on the order of several micrometers.Namely, the expandable film 221 is bonded to the rear face 17 of thesilicon wafer 11 by way of the die-bonding resin layer 223. A filmexpanding means 30 is attached to a peripheral part of the expandablefilm 221. After bonding the die-bonding-resin-attached film 220, theprotective film 18 is peeled off from the front face 3 side of thesilicon wafer 11 as shown in FIG. 26B, and the expandable film 221 isirradiated with UV rays as shown in FIG. 26C. This hardens theUV-curable resin layer, which is an adhesive layer in the expandablefilm 221, thereby making it easier for the die-bonding resin layer 223to peel off from the expandable film 221.

Subsequently, as shown in FIG. 27A, the film expanding means 30 pullsthe peripheral part of the expandable film 221 outward, so as to expandthe expandable film 221. Expanding the expandable film 221 causesfractures to start from the cutting start regions 8 and reach the frontface 3 and rear face 17 of the silicon wafer 11. As a consequence, thesilicon wafer 11 is cut along the lines to cut 5 with a high precision,whereby a plurality of semiconductor chips 25 each including onefunctional device 215 are obtained. Here, the opposing cut sections 25a, 25 a of the neighboring semiconductor chips 25, 25 are separated fromeach other from their close contact state as the expandable film 221expands, whereby the die-bonding resin layer 223 in close contact withthe rear face 17 of the silicon wafer 11 is cut along the lines to cut 5together with the silicon wafer 11.

Next, using a vacuum collet or the like, the semiconductor chips 25 aresuccessively picked up as shown in FIG. 27B. Here, the die-bonding resinlayer 23 is cut into outer forms similar to those of the semiconductorchips 25, whereas the adhesive force between the die-bonding resin layer223 and expandable film 221 is lowered, whereby each semiconductor chip25 is picked up while in a state where the cut die-bonding resin layer223 is attached to its rear face. Then, as shown in FIG. 27C, thesemiconductor chip 25 is mounted on a die pad of a lead frame 27 by wayof the die-bonding resin layer 223 closely in contact with the rearface, and is joined thereto with the filler upon heating.

In the foregoing method of cutting the silicon wafer 11, the siliconwafer 11 having the front face 3 formed with the functional devices 215is used as an object to be processed, and is irradiated with laser lightL while using its rear face 17 as a laser light entrance surface andlocating the light-converging point P within the silicon wafer 11. Thisgenerates multiphoton absorption within the silicon wafer 11, therebyforming the cutting start regions 8 caused by the molten processedregions 13 within the silicon wafer 11 along the lines to cut 5. Here,the rear face of the semiconductor substrate is used as the laser lightentrance surface, since there will be a fear of the functional devicesinhibiting the laser light from entering if the front face is used asthe laser light entrance surface. When the cutting start regions 8 areformed within the silicon wafer 11 as such, fractures can start from thecutting start regions 8 naturally or with a relatively small forceapplied thereto, so as to reach the front face 3 and rear face 17 of thesilicon wafer 11. Therefore, when the expandable film 221 is bonded tothe rear face 17 of the silicon wafer 11 by way of the die-bonding resinlayer 223 and expanded after forming the cutting start regions 8, thecut sections 25 a, 25 a of the silicon wafer 11 cut along the lines tocut 5 are separated from each other from their close contact state. As aconsequence, the die-bonding resin layer 223 existing between thesilicon wafer 11 and expandable film 221 is also cut along the lines tocut 5. Therefore, the silicon wafer 11 and die-bonding resin layer 223can be cut along the lines to cut 5 much more efficiently than in thecase cut with a blade or the like.

Since the cut sections 25 a, 25 a of the silicon wafer 11 cut along thelines to cut 5 are initially in close contact with each other, the cutpieces of silicon wafer 11 and cut pieces of die-bonding resin layer 223have substantially the same outer form, whereby the die-bonding resin isprevented from protruding from the cut sections 25 a of the pieces ofthe silicon wafer 11.

Further, before forming the cutting start regions 8 within the siliconwafer 11, the rear face 17 of the silicon wafer 11 is ground such thatthe silicon wafer 11 attains a predetermined thickness. When the siliconwafer 11 is thinned to a predetermined thickness as such, the siliconwafer 11 and die-bonding resin layer 223 can be cut along the lines tocut 5 with a higher precision.

INDUSTRIAL APPLICABILITY

As explained in the foregoing, the method of cutting a semiconductorsubstrate in accordance with the present invention can efficiently cutthe semiconductor substrate together with a die-bonding resin layer.

1-3. (canceled)
 4. A method of cutting a semiconductor substrate, themethod comprising the steps of: irradiating a semiconductor substratehaving a sheet bonded thereto with laser light having a wavelength thatenables the laser light to transmit through the semiconductor substrate,such that grooves are not formed on a laser incident surface of thesemiconductor substrate by irradiation of the laser light and no moltenregion is formed on the laser incident surface of the semiconductorsubstrate, while locating a light-converging point within thesemiconductor substrate, so as to form a modified region only within thesemiconductor substrate, such that the modified region is a moltenprocessed region separated from the laser incident surface in athickness direction of the semiconductor substrate, the modified regionforming a part of the semiconductor substrate to be cut; and expandingthe sheet after forming the part of the semiconductor substrate to becut, by pulling peripheral portions of the sheet outwardly, so as to cutand separate at least the semiconductor substrate along the part to becut. 5-18. (canceled)
 19. A method of manufacturing a semiconductordevice formed using a method of cutting a semiconductor substrate, themanufacturing method comprising: irradiating a semiconductor substratehaving a sheet bonded thereto and having a surface formed with at leastone semiconductor device with laser light having a wavelength thatenables the laser light to transmit through the semiconductor substrate,such that grooves are not formed on a laser incident surface of thesemiconductor substrate by irradiation of the laser light and no moltenregion is formed on the laser incident surface of the semiconductorsubstrate, while locating a light-converging point within thesemiconductor substrate, so as to form a modified region only within thesemiconductor substrate, such that the modified region is a moltenprocessed region separated from the laser incident surface in athickness direction of the semiconductor substrate, the modified regionforming a part of the semiconductor substrate which is to be cut; andexpanding the sheet after forming the part which is to be cut by pullingperipheral portions of the sheet outwardly, so that a gap is formedbetween the divided parts of the semiconductor substrate, and so as tocut and separate at least the semiconductor substrate along the partwhich is to be cut, with such cutting thereby providing at least onemanufactured semiconductor device.